Disclosed herein are curable inks and methods for the use thereof. More specifically, disclosed herein are inks that are curable upon exposure to actinic radiation and that absorb radiation in the infrared region.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Radiation curable inks generally comprise at least one curable monomer, a colorant, and a radiation activated initiator that initiates polymerization of curable components of the ink. Radiation-curable inks can be employed in ink jet printing systems. Radiation-curable phase-change inks are known as well, as disclosed in, for example, U.S. Pat. Nos. 7,153,349, 7,259,275, 7,270,408, 7,271,284, 7,276,614, 7,279,506, 7,279,587, 7,293,868, 7,317,122, 7,323,498, 7,384,463, 7,449,515, 7,459,014, 7,531,582, 7,538,145, 7,541,406, 7,553,011, 7,556,844, 7,559,639, 7,563,489, 7,578,587, 7,625,956, 7,632,546, 7,674,842, 7,681,966, 7,683,102, 7,690,782, 7,691,920, 7,699,922, 7,714,040, 7,754,779, 7,812,064, and 7,820,731, the disclosures of each of which are totally incorporated herein by reference. Radiation-curable phase change inks can exhibit additional desirable characteristics such as improved hardness and scratch-resistance and improved adhesion to various substrates. Radiation-curable gel inks can also exhibit advantages in that dot spread of the ink can be controlled, the ink does not bleed excessively into the substrate.
To maintain brand integrity of a radiation-curable ink, one must be able to identify the brand name ink with authenticity. However, with a radiation curable ink such as an ultraviolet (UV) curable ink, for example, since the ink is absorbing in the UV range, using additive materials with absorbance profiles in the same region to achieve spectroscopic monitoring is undesirable. It is preferred that such special additive materials are not visible (covert) and have a unique absorbance profile. Furthermore, it is desirable to be able to check the ink for brand authenticity both before printing and curing as well as after printing and curing. Typically, UV-active additives like fluorescent materials are widely used for providing security to ink and printed documents. However, they are not desirable for use with UV-curable inks for authentication because the uncured ink will cure in the act of authentication. Moreover, these UV-active additives may not be stable in the ink composition. Therefore, a need exists for covert, non-reactive taggants in radiation-curable inks that can be detected in both the uncured and the cured, printed ink. In one specific embodiment, it is desirable that the chosen taggant material survive the radiation-curing step essentially unaltered.